3.5 Effects of Heavy Metals in Corals
61
3.5 Effects of Heavy Metals in Corals
The recorded metal concentrations in the corals are high and this is generally
attributed to the substitution mechanism of the metals into the crystal lattice; the
adsorption process; trapping up of the particulate matter into the aragonite lattice
and the uptake of organic matter from the coral tissues and feeding through polyps.
The free ionic form of metals is the most toxic and bioavailable, and therefore toxicity becomes higher in oligotrophic waters where complexation opportunities are
few. Marques et al. (2019) highlighted that metal pollution is a common local scale
impact on coral reefs. Nonetheless, sensitivity to trace metals is dependent on a
variety of physiological and biochemical factors that are specific to each species
as well as external factors such as the duration of exposure (Hudspith et al. 2017).
Potential factors such as impaired sperm activation and motility, changes in egg
membrane permeability and conductivity, and elevated intracellular reactive oxygen
species affect the biochemical and cellular mechanisms of action underlying trace
metal toxicity to external fertilisation (which is yet to be fully understood) (review
by Hudspith et al. 2017).
Once incorporated within the coral, heavy metals can result in acute or chronic
toxicity causing lethal effects or long-term impacts to key biological processes of
corals. The key biological processes which are affected include: respiration (Howard
et al. 1986); fertilization, metamorphosis and larvae settlement, larvae survival
and motility (Goh 1991; Reichelt-Brushett and Harrison 2000; Negri and Heyward
2001; Reichelt-Brushett and Harrison 2004; Reichelt-Brushett and Harrison 2005;
Mitchelmore et al. 2007); and complete inhibition of fertilization in Goniastrea
aspera, Favites chinensis and Platygyra ryukyuensis gametes when exposed to copper
sulphate solutions greater than or equal to 0.5 mg/L (Heyward 1988). The lethal
effects on corals include: reduced growth (Howard and Brown 1987); mucus secretion (Wooldridge 2009); physiological stress (Howard and Brown 1984); loss of
zooxanthellae and photosynthetic efficiency in adult corals (Esquivel 1986; Harland
and Brown 1989; Harland and Nganro 1990; Jones 1997; Bielmyer et al. 2010;
Biscéré et al. 2015); enhanced mortality (Mitchelmore et al. 2007); and reduced
biodiversity (Ramos et al. 2004).
Observations by author (s) on the differential effects of heavy metals on corals
include: Vaschenko et al. (1999), who mentioned that trace metals also interfere
with calcium cation exchange and membrane permeability; Biuki et al. (2010),
who mentioned that normal behaviour is affected; Thongra-ar (1997), Vaschenko
et al. (1999), and Reichelt- Brushett and Harrison (2005); who stated that heavy
metals delay or inhibit normal reproduction and early-life-stage development in
many marine invertebrates; Richmond (1997), who stated that exposure to excess
trace metal concentrations, interferes with many cellular processes; Thompson et al.
(1980) Hughes et al. (2005), and Negri et al. (2005) have observed tissue retraction
as a cnidarian stress response.
Stress could also be a behavioral response allowing the detachment of tissue
and the escape of coral polyps from the skeleton; van Dam et al. (2011) highlighted
61
3.5 Effects of Heavy Metals in Corals
The recorded metal concentrations in the corals are high and this is generally
attributed to the substitution mechanism of the metals into the crystal lattice; the
adsorption process; trapping up of the particulate matter into the aragonite lattice
and the uptake of organic matter from the coral tissues and feeding through polyps.
The free ionic form of metals is the most toxic and bioavailable, and therefore toxicity becomes higher in oligotrophic waters where complexation opportunities are
few. Marques et al. (2019) highlighted that metal pollution is a common local scale
impact on coral reefs. Nonetheless, sensitivity to trace metals is dependent on a
variety of physiological and biochemical factors that are specific to each species
as well as external factors such as the duration of exposure (Hudspith et al. 2017).
Potential factors such as impaired sperm activation and motility, changes in egg
membrane permeability and conductivity, and elevated intracellular reactive oxygen
species affect the biochemical and cellular mechanisms of action underlying trace
metal toxicity to external fertilisation (which is yet to be fully understood) (review
by Hudspith et al. 2017).
Once incorporated within the coral, heavy metals can result in acute or chronic
toxicity causing lethal effects or long-term impacts to key biological processes of
corals. The key biological processes which are affected include: respiration (Howard
et al. 1986); fertilization, metamorphosis and larvae settlement, larvae survival
and motility (Goh 1991; Reichelt-Brushett and Harrison 2000; Negri and Heyward
2001; Reichelt-Brushett and Harrison 2004; Reichelt-Brushett and Harrison 2005;
Mitchelmore et al. 2007); and complete inhibition of fertilization in Goniastrea
aspera, Favites chinensis and Platygyra ryukyuensis gametes when exposed to copper
sulphate solutions greater than or equal to 0.5 mg/L (Heyward 1988). The lethal
effects on corals include: reduced growth (Howard and Brown 1987); mucus secretion (Wooldridge 2009); physiological stress (Howard and Brown 1984); loss of
zooxanthellae and photosynthetic efficiency in adult corals (Esquivel 1986; Harland
and Brown 1989; Harland and Nganro 1990; Jones 1997; Bielmyer et al. 2010;
Biscéré et al. 2015); enhanced mortality (Mitchelmore et al. 2007); and reduced
biodiversity (Ramos et al. 2004).
Observations by author (s) on the differential effects of heavy metals on corals
include: Vaschenko et al. (1999), who mentioned that trace metals also interfere
with calcium cation exchange and membrane permeability; Biuki et al. (2010),
who mentioned that normal behaviour is affected; Thongra-ar (1997), Vaschenko
et al. (1999), and Reichelt- Brushett and Harrison (2005); who stated that heavy
metals delay or inhibit normal reproduction and early-life-stage development in
many marine invertebrates; Richmond (1997), who stated that exposure to excess
trace metal concentrations, interferes with many cellular processes; Thompson et al.
(1980) Hughes et al. (2005), and Negri et al. (2005) have observed tissue retraction
as a cnidarian stress response.
Stress could also be a behavioral response allowing the detachment of tissue
and the escape of coral polyps from the skeleton; van Dam et al. (2011) highlighted